Modern modular converter topologies with multilevel characteristics consist of identically-constructed functional units, which are referred to as submodules. Submodules are constructed either as half bridge or full bridge submodules. These are connected in series with one another to provide an inverter phase. The interconnection of a plurality of half bridge submodules in series takes up a lot of space. This makes for high costs of the converter.
In low-voltage applications it is usual to construct modular topologies from circuit board-based submodules with discrete power semiconductor switching elements. The use of circuit boards leads to further problems caused by the limited current carrying capacity of the circuit boards and the inferior cooling conditions when compared to power modules in which the power semiconductor switching elements are attached directly to a circuit carrier (so-called Direct Copper Bonding (DCB)). Significant heat losses due to current, which must be dissipated, occur in the connecting cables and at the contact points between connecting cables and circuit boards.
The electrical connection between the discrete power semiconductor switching elements and the screw contacts or clamp contacts of the cables may include copper tracks on the circuit carriers. To guarantee the current carrying capability needed, more expensive high-current circuit carriers are used. These are known as thick copper boards or as boards with inserted copper profiles.
The heat in a circuit board-based converter is removed directly at a main terminal (the drain or collector terminal of the power semiconductor switching element). To do this the power semiconductor switching element is pressed directly with its terminal contact over a large surface against a heat sink. To avoid an electrical connection between the terminal contact and the heat sink, an insulator is arranged between these two surfaces.
The heat lost due to current in the connecting cables and at the contact points can be minimized and dissipated through larger cable cross sections and larger contacts. Once again however this leads to the mounting technology and connection technology consequently being very large and heavy. Despite this, the circuit board-based realization of a converter is frequently preferred to DCB-based converters, since such a converter has better electrical characteristics.